Use of heating or energy radiating devices, particularly microwave radiating devices, to administer heat for the treatment of various diseases of the prostate have been demonstrated to provide efficacious treatment of various prostate conditions (Devonec et al., Monographs in Urology, 13, 77-95 (1992); De La Rosette et al., J. Urology, 157, 430-438 (1997); Devonec et al., J. Endourology, 5, 129-135 (1991); Bernier et al., Curr. Opin. Urol., 7, 15-20 (1997)). Research has indicated that the cellular transformations brought about by raising tissue temperatures above certain levels can be used therapeutically. At temperatures above 45.degree. C., thermal damage has been found to occur to cells, even when the exposure to the elevated temperatures lasts for even a short period of time. Thermal therapy has been defined as the process of heating tissue to greater than 45.degree. C. to create necrosis. Both normal and abnormal cells respond to thermal exposure. Accordingly, therapies using heat have relied on healthy tissue regeneration after the delivery of a "thermal dose." A thermal dose is a quantity which is indicative of the biological impact of elevated temperature maintained for a period of time. For the purposes of the present invention, thermal dosages can be calculated according to the method of Sapareto et al., International Journal of Radiation Oncology, Biology, Physics, 10, 787-800 (1984), except that the breakpoint of 45.degree. C., rather than 43.degree. C. is used for non-malignant tissues. That is, for the purposes of the present invention, thermal dose measured in Equivalent 45.degree. C. hours is equal to the sum of the products of one-half of the treatment temperature in excess of 45.degree. C. times the duration at that time, or ##EQU1##
wherein T is temperature in degrees centigrade and t is time in hours.
A variety of different methods have been developed to deliver therapeutically effective quantities of heat to the prostate, including ultrasound delivery devices, RF delivery devices and hot water-recirculating catheters. One such device is the "WITT" hot water recirculating catheter, which is manufactured by ArgoMed, Inc. of Parsippany, New Jersey (USA). Another such device is the "Thermex II", which is manufactured by Direx Systems, Ltd. While hot water recirculating catheters are useful in the context of the present invention, a significant drawback is that it is difficult to apply an accurate thermal dose to the prostatic urethra while simultaneously avoiding delivery of a therapeutic dose of heat to non-target tissues such as the penis. Moreover, the design of hot water recirculating catheters can make accurate placement of the heating zones within the patient more difficult. A limitation to the usage of RF applicators is their relatively poor ability to penetrate tissue, often resulting in superficial treatment of the prostatic tissue.
A more preferred method to deliver thermotherapy in the context of the present invention is via a urethrally-inserted catheter with an imbedded microwave antenna. A cooling device is typically incorporated into microwave emitting catheters so that urethral tissue proximal to the microwave antenna is cooled. The addition of this feature has been directed at preserving the prostatic urethra, thereby reducing treatment discomfort and post-treatment recovery time. A temperature or energy measurement device can be used during treatments so that a thermal dose can be measured. Treatments utilizing this approach include TransUrethral Microwave Thermotherapy (TUMT). One disease currently treated by TUMT is Benign Prostatic Hyperplasia (BPH). The therapeutic effect of such therapies can be measured in any suitable manner. For example, therapy can be measured by an improvement in the AUA symptom score, or by an improvement in the Madsen-Iversen score, an improvement in urine flow, an improvement in urethral diameter, or the like.
The objective of TUMT of BPH is to destroy a portion of the prostatic tissue, while preserving the tissue immediately adjacent to the prostatic urethra and the tissue immediately adjacent to the same. Current opinion in the field is that the greater the tissue destruction in the prostate, the more beneficial the treatment (De La Rosette et al., supra). Therefore, current device and therapy design is directed at improving the maximum heat dose over the shortest period of time. In that regard, typical maximum temperatures frequently reach 65.degree. C. or greater within the prostate. Unfortunately, this has a number of undesirable side-effects. For example, with prior art TUMT methods, hematuria rates typically exceed 30%, rates of urinary retention requiring long term catheterization usually exceeds 20%, rates of urethral bleeding not merely due to catheterization exceed 5%, and rates of urinary tract infection, ejaculatory disturbances, inflammation in the urethra, chronic incontinence, and impotence are all statistically significant and exceed about 1.5%.
There are, however, other delivery methods which utilize non-cooled radiation applicators and require the delivery of multiple treatments at relatively low temperatures (45.degree. C.-47.degree. C. and lower). The objective of these methods is to obtain a therapeutic benefit while avoiding temperature ranges that are commonly thought to cause patient intolerance and give rise to significant side effects. The problem with these methods is that the data suggest, and current published opinion in the art states, that efficacy is reduced. In addition, multiple treatment sessions are required at these relatively low temperatures which is inconvenient and uncomfortable for the patient and economically disadvantageous for the physician.
One significant drawback to other TUMT devices and therapies is that they are frequently painful for the patient and require the use of narcotic analgesics to control pain. This makes current TUMT inconvenient, limits the use of the therapy, adds to the expense and recovery time, and can potentially result in patient loss.
A further drawback to other TUMT devices is the requirement for multiple treatment sessions and its limited efficacy. Thus, the economics of the treatment are severely limited.
The electromagnetic radiation applicator systems developed for the treatment of BPH have limited the ability of the skilled artisan to control urethral and prostate temperatures. Many prior art radiation applicator devices have controlled the heating of the prostate by simply controlling the power supplied to the heating unit. This method of controlling the heating is typically necessary when the catheter system is used in conjunction with a surface cooling device, because the surface cooling device alters measured temperatures. Non-cooled catheter systems (see, e.g., U.S. Pat. No. 4,967,765 to Turner et al.) have the ability to monitor surface temperatures more accurately than cooled catheter systems. However, these devices have also been constructed in a manner to limit complexity and cost. Accordingly, prior art catheter systems have been capable of heating tissue to a pre-selected temperature and maintaining the tissue at that temperature, but have not incorporated the more advanced features of the present invention. Other catheter designs useful in the context of the present inventive system have been commercially developed, e.g., by EDAP/Technomed and Urologix. While these other catheter designs are well known in the art, other examples are disclosed, e.g., by U.S. Pat. Nos. 4,620,480 and 5,628,770.
In view of the foregoing problems, there is a need for prostatic thermotherapy, particularly for BPH that is cost-effective, eliminates the use of general anesthesia and obviates the need for a cooled catheter. There is also a need for a prostatic thermotherapy that reduces non-beneficial side effects of previous methods.
The present invention provides such a method and related devices. These and other advantages of the present invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.